/Engine/Plugins/Experimental/PCG/Source/PCG/Public/Elements/Metadata/PCGMetadataRotatorOpElement.h
Taken from Kismet Math Library.
namespace PCGMetadataRotatorHelpers { FRotator PCGMetadataRotatorHelpers::RLerp ( const FRotator & A, const FRotator & B, double Alpha, bool bShortestPath ) }